Wash the potatoes and put them in your pressure cooker. Pour in enough water to immerse them fully. Cover with lid and set on high heat.
As soon as you hear the first whistle, turn down the heat and let cook slowly for 10 minutes.
Now switch off the heat and let the cooker cool down naturally.
In the meantime, peel and chop the onion to thin slivers and set aside.
Cut each green chili tangentially into 2 or 3 pieces and set aside.
Check to see if the steam has subsided in the cooker. If yes, open the lid and drain off the hot water. Fill up with tap water, keep for a minute and drain again.
Refill with tap water, take out the potatoes one by one and peel off the jackets with your fingers.
Transfer to a mixing bowl and mash lightly with the bottom of a stainless steel glass so that some lumps remain to lend texture to the bhaji.
To cook:
Set a thick wok or deep pan on high heat. Pour in the cooking oil and throw in the mustard seeds.
As soon as the mustard seeds are about to finish crackling, tip in the urud dal and lower the heat. Stir for a few moments.
As soon as the dal starts to turn a light brown, throw in the chopped chilies.
Pull the curry leaves off their sprigs and toss them in. Stir once and put in the chopped onions and the ginger.
Turn up the heat and stir continuously till the onions turn a light brown in color.
Now tip in the mashed potatoes and pour in the water. Add the salt and the turmeric powder. Stir occasionally till it comes to a boil. A minute later, switch off the heat.
If you are using coriander leaves, you can break / chop them and garnish. So too, pepper lovers can sprinkle the pepper powder. Stir and cover with a lid.
Serve bhaji hot with puris, chappatis, rotis, naans, porottas or with crisp dosas. Enjoy!